intermetallic compounds? 1

[bmoorthy]

Hello All

This terminology(intermetallic compounds) keeps coming up when ever somebody expresses the detoriation of desired Corrosion resistance properties or mechanical properties.

Is Sigma Phase: Intermetallic Compound?

How to identify the Intermettalic compound in high Nickel alloys
Are there any acceptance level.(Based on ASTM Standards)
Somebody suggested Micro hardness as an indicator of the presence.
Does intermettalic compounds have high hardness.

 

[metengr]

Yes, sigma phase is a secondary phase and would be considered an intermetallic compound of the chemical form AB consisting of combinations of (Cr, Fe, Mo, Ni). Other intermetallic compounds that form in stainless steel or even nickel-base alloys are;

chi phase
alpha prime
Laves phase
R phase
Tau phase

Carbides are considered precipitates and are of the form M(x)C or M(x)N
For example;
M(6)C carbide
M(23)C(6) chromium carbide of the type [Cr,Fe,Mo](23)C(6)
M(2)N nitride
MC Ti(CN), titanium carbonitride

Yes. Review ASTM A 923. This method is applicable to evaluating the solution heat treatment effectiveness of duplex stainless steel alloys.

The detection of intermetallic phases in nickel-base alloys can be by several methods;

bend testing
impact testing
chemical etching or
corrosion testing

The acceptable level of intermetallic phase in nickel-base alloys from either exposure to ageing in service or improper heat treatment would be by mechanical test methods and by corrosion testing.